Glycolysis

Glucose is a sugar that is taken up that from our diet. Carbohydrates are broken down in the digestive system to glucose. When glucose is broken down a large amount of energy is released. The glycolysis is a series reactions that forms the beginning of the break down of glucose. The word glycolysis comes from glucos (meaning sugar) and lysis (meaning break down). These series of reactions are found in almost all forms of life on this earth. In the glycolysis, glucose is broken down to pyruvate in 10 steps. Each reaction is regulated by another enzyme. Here you can find the series of reactions with the regulating enzymes.

The glycolysis

The Glycolysis in structural formulas

The glycolysis

                                                                       Glucose
                                                                         
                                                             Glucose 6-phosphate
                                                                                                
                                                           Fructose 6-phosphate
                                                                         
                                                        Fructose 1,6-bisphosphate
                                                         
                            Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate
                                                                                                   
                                                                                    1,3-Bisphosphoglycerate
                                                                                                   
                                                                                       3-Phosphoglycerate
                                
                                                                                         2-Phosphoglycerate
                                                                                                   
                                                                                         Phosphoenolpyruvate
                                                                                                    
                                                                                                  Pyruvate

Pyruvate can become further oxidised in the citric acid cycle, or be transformed to lactic acid. Each time when in a reaction ATP becomes transformed in ADP it means that energy was necessarily for this reaction to take place, this energy was obtained from the ATP molecule by taking one phosphate off. In a reaction where the opposite transformation occurs (ADP to ATP) it means that energy is released by the reaction and this energy is stored in the ATP. In a reaction where NAD + is transformed into NADH also energies are released and becomes stored in the NADH molecule. This stored energy can become uses for many processes in the cell.
Be aware that the part after the junction of Fructose 1,6-bisphosphate counts double to respect of the first part, because here the 6 carbon sugar is divided in 2 pieces of 3 carbon atom sugars.